1. Field of the Invention
The present invention relates to a method of making a thermoplastic mandrel which can subsequently be used in the manufacture of hose. This invention also relates to a mandrel made by such a method,
2. Prior Art Statement
Ordinarily, when making hose by the mandrel method, a wire mandrel is used. Wire has the disadvantages that it is relatively expensive to use, is heavy, and if damaged or worn, it cannot be easily returned to a usable condition. It has been found, on the other hand, that a mandrel made of thermoplastic material can be made having suitable characteristics with regard to rigidity, stiffness, and flexibility such that it is suitable for use in place of a wire mandrel in most applications. A mandrel made of thermoplastic material has the advantage that the mandrel is lighter than the corresponding wire mandrel, it is cheaper to produce, and when said mandrel is damaged or worn, the thermoplastic material can be easily reformed to produce a new mandrel.
In producing a thermoplastic mandrel, it has been found that it is very difficult to splice thermoplastic rods to produce a mandrel of suitable length. Melt bonding or butt welding two mandrel ends by pressing them against a hot surface and then pressing them together. leaves too much flash, which must be trimmed off, on the mandrel joint.
When using a hot melt adhesive, which is applied between two thermoplastic rod ends, the ends of the thermoplastic rods have to be cut perfectly flush and perpendicular to the longitudinal axis of the mandrel. Any variation from the perpendicular, or gaps between the rod ends produces an incomplete bond. In addition, there is not enough mass in a melt adhesive film for sufficient interaction with the electrical induction field used in induction molding. This makes it necessary to use high energies in the induction field which in turn causes too rapid heating and subsequent burning of the adhesive. Also, the large mass of the mandrel, when compared with the small mass of the adhesive used, results in the phenomenon that the mandrel acts as a heat sink, and the mandrel does not get hot enough to melt, while the adhesive gets so hot that it burns. It has been found that induction heated hot melt adhesive films bond thermoplastic polyester mandrels only one time in twenty.
It is known to use heat generating particles in an electric inductive field to produce a bond in plastic hose and similar items as is illustrated by Heller et al in U.S. Pat. Nos. 3,574,031; 3,945,867; and 4,067,765; and 4,000,760.
A method for producing heat sealing and bonding using a magnetic induction method, and the products produced thereby are described by James in U.S. Pat. Nos. 3,461,014 and 3,709,775.
A composition adapted for inductive heating and a method for using the same is described by Kohler in U.S. Pat. No. 2,393,541.
Adhesives employing non-corrosive ferromagnetic particles which are used to bond thermoplastics by the use of inductive heating are described by Guglielmo et al in U.S. Pat. Nos. 3,620,875 and 3,620,876.
It is known to disperse inductively activated material in the body of an object that is subsequently to be attached to a plastic fitting as is disclosed by Leatherman in U.S. Pat. No. 3,923,580.
Other patents that deal closely with the bonding of thermoplastics include the following: U.S. Pat. Nos. 2,700,634; 3,462,336; 3,396,258; 3,802,985; 3,462,336; 3,996,090; 4,239,575; 3,900,360; 3,941,641; 4,029,837; 4,035,547; 3,528,867; 3,802,985; 3,941,641; 3,902,940; and Canadian Pat. No. 1,125,155.